1. Field of the Invention
The present invention relates to a toner density sensor, and an ink jet head, a developing unit and an image forming apparatus in which a toner density sensor is used, and more particularly to a toner density sensor for a wet type image forming apparatus such as a printer, a facsimile or a copying machine, and an ink jet head, a developing unit and an image forming apparatus in which a toner density sensor is used.
2. Description of the Related Art
A wet type image forming apparatus uses liquid developer composed of toner dispersed in solution to develop an electrostatic latent image formed on a photosensitive member to form a visible toner image. In the wet type image forming apparatus, the toner density, that is, the ratio of the toner in the liquid developer, has a very serious influence on the image density, chapping, the resolution and so forth of the developed image. Meanwhile, since the toner in the liquid developer is gradually consumed as development is repeated, in order to always keep an appropriate toner density, the toner density is measured and, when the density drops, either warning information of this is developed or a suitable amount of toner or liquid developer of a high density is automatically supplemented.
Thus, a toner density sensor is required to measure the toner density in order to keep the toner density appropriate. One of such toner density sensors is disclosed in Japanese Patent Publication No. 21435/1966 wherein liquid developer is flowed in a passage formed from a transparent member and an amount of transmission light through the liquid developer is measured by means of a light emitting element and a light receiving element disposed in an opposing relationship to each other on the opposite sides of the passage and is utilized as a substitute characteristic of the toner density.
The toner density sensor, however, is disadvantageous in that toner density detection of an appropriate density is difficult. The reason is that, since liquid developer of an, appropriate density is very low in transmission factor, the transmission light through the liquid developer is attenuated by a large amount by the liquid developer. Further, if the light path length through the liquid developer is reduced in order to allow toner density detection of an appropriate density, then retention of the toner in the liquid developer or clogging of the passage with foreign articles in the light path becomes liable to occur and toner becomes liable to stick to the passage in the light path.
It is an object of the present invention to provide a toner density sensor by which, where light emitted from a light emitting element is passed through developing liquid and received by a light receiving element so that a density of the liquid developer may be detected from an output of the light receiving element, toner density detection of an appropriate density can be performed readily also with liquid developer whose transmission factor in a density upon measurement is very low.
In order to attain the object described above, according to an aspect of the present invention, there is provided a toner density sensor, comprising a light emitting element, a light receiving element for receiving light emitted from the light emitting element, a liquid developer tank for accommodating liquid developer therein, a diluting liquid tank for accommodating diluting liquid therein, a mixing chamber for mixing the liquid developer and the diluting liquid at a certain fixed ratio, a passage for forcedly circulating the diluted liquid developer, a transparent cell element disposed in the passage between the light emitting element and the light receiving element for allowing the light emitted from the light emitting element to be transmitted through the fluid passing the inside thereof so that an amount of the transmission light through the fluid may be measured by means of the light emitting element and the light receiving element, and means for detecting a density of the liquid developer based on the transmission light amount through the diluted liquid developer in the mixing chamber provided by an output of the light receiving element.
The toner density sensor is advantageous in that, even where the liquid developer has a very low transmission factor in a density upon measurement, toner density detection of an appropriate density can be performed readily. The reason is that, since the liquid developer is diluted normally at a certain fixed ratio, toner density detection within a density range within which the transmission light is attenuated but by a small amount can be performed even with a light path length, within which retention of toner or clogging with foreign articles in the liquid developer does not occur in the light path.
Preferably, the diluting liquid is a solution the same as a base material of the liquid developer.
Preferably, the light emitting element and the light receiving element are covered completely with a transparent member having a low surface energy property and are disposed in an opposing relationship to each other with a certain fixed gap left therebetween in the mixing chamber.
According to another aspect of the present invention, there is provided an ink jet head, comprising any of the toner density sensors described above.
According to a further aspect of the present invention, there is provided an image forming apparatus, comprising the ink jet head described above.
According to a still further aspect of the present invention, there is provided a developing unit, comprising means for making the density of the liquid developer fixed based on the density of the liquid developer detected by any of the toner density sensors described above
According to a yet further aspect of the present invention, there is provided an electrophotographic image forming apparatus, comprising charging, exposure, transfer and fixing means, and the developing unit described above.
The above and other objects, features and advantages of the present invention will become apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings in which like parts or elements are denoted by like reference symbols.